Half-wave symmetry selective harmonic elimination method for multilevel voltage source inverters

This study investigates in detail the properties of multiple solutions of different existing selective harmonic elimination (SHE)-pulse-width modulation (PWM) schemes for multilevel voltage source inverters. In order to obtain more solutions to SHE-PWM problems, a novel half-wave symmetry SHE modulation method and its generalised formulation are proposed. The advantages of the proposed formulation include simplicity in format, flexibility in PWM waveforms and a broad solution space. Taking a five-level inverter with 20 points in half a cycle as an example, 12 groups of solutions at modulation index (M) of 0.8 are obtained and illustrated. A set of solutions for M varying from 0 to 1.15 are also listed in forms of initial values and their effective regions. Simulations on a Psim platform are carried out. An experimental prototype with a five-level cascade voltage source inverter topology is built and investigated. The experimental results agree well with simulated ones, which prove the validity and practicability of the new method.